Skeletal muscle function declines with age. With the increase in man?s average expected life span and the increasing elderly population worldwide, scientific research is attempting to preserve the aging population?s quality of life. One theory at the forefront of explanations for the effects of aging has been the cumulative negative effects of free radical production over time. Evidence suggests that aged organisms grow increasingly vulnerable to damage from reactive oxygen species (ROS). In addition to the progressive atrophy and functional declines observed in aging skeletal muscle, common medical conditions in the elderly such as respiratory and circulatory insufficiencies can compromise the body?s ability to deliver oxygen to tissues throughout the body. These combined effects of aging and hypoxia on skeletal muscle car severely compromise functional capacity in these individuals and further hasten the loss of physical independence. I propose to use the single skeletal muscle fiber model in which experimental conditions can be tightly controlled and several intracellular factors can be examined in an intact, contracting fiber. By I studying the alterations that occur in the aged muscle?s oxidative stress and its ability to respond to exercise and hypoxia, a better understanding of how exercise prescription and drug therapy can prevent or improve muscle function with age may be achieved.